Which statement is correct about the forwarding table?
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A. B. C. D.C
The forwarding table is an essential component of a router's operation, which is used to determine the outgoing interface and next hop for a given packet based on its destination IP address. Let's examine each statement in detail to identify the correct one:
A. The forwarding table is stored only on the PFE.
The Packet Forwarding Engine (PFE) is responsible for the actual forwarding of packets through the router's interfaces. However, it does not store the entire forwarding table. Instead, the PFE stores only a portion of the forwarding table that is relevant to the interfaces it is responsible for forwarding packets to. Therefore, statement A is incorrect.
B. The forwarding table contains all known routes.
The forwarding table contains the routes that have been learned by the router through various means, such as static configuration or dynamic routing protocols like OSPF, BGP, or RIP. However, the forwarding table does not necessarily contain all known routes because there may be routes that are not currently being used or that have been filtered out for some reason. Therefore, statement B is incorrect.
C. The forwarding table is stored on both the RE and PFE.
The forwarding table is stored in two locations within a Junos router: the Routing Engine (RE) and the PFE. The RE is responsible for maintaining the entire forwarding table, including all known routes, while the PFE stores only the portion of the forwarding table relevant to its interfaces. When a packet arrives at a router, the RE consults the forwarding table to determine the appropriate outgoing interface and next hop, and then sends this information to the PFE for forwarding. Therefore, statement C is correct.
D. The forwarding table is stored only on the RE.
This statement is incorrect because, as mentioned above, the forwarding table is also stored on the PFE. The RE maintains the complete forwarding table, but it is also distributed to the PFEs as necessary to enable efficient packet forwarding. Therefore, statement D is incorrect.
In summary, the correct statement about the forwarding table is that it is stored on both the RE and PFE.